April, 2005

EEEL Researchers Develop Low-Cost Methods for Characterizing Projection Display Systems

Measurement of electronic displays, particularly projection displays, can be affected by ambient stray light such as veiling glare. Veiling glare results from light outside of the measurement area scattering off of lens surfaces, barrels, irises, and glass defects producing an overall increase in luminance in the measurement apparatus (and thus reduction in contrast) that does not exist in the original image. Ambient sources can also contribute to the measurement environment. These include room lights directly illuminating the screen and the reflection of these light sources off walls, floors, furniture, and other objects. Back reflections from the image on the projection screen must be considered as well. These reflections and lights affect the image, masking the intrinsic luminance (or luminous flux) and contrast of the projection display.

Despite good intentions, significant errors can be introduced if the effects of stray light on spatial resolution are not accounted for. In many cases prohibitively expensive cameras and complex software may not be necessary to adequately characterize a display's performance with the introduction of inexpensive tools that EEEL researchers, Paul Boynton and Ed Kelley, have developed. These inexpensive tools include frustrum masks, stray light elimination tools (SLETs), replica masks, and projection masks. A recent paper by Boynton and Kelley compared the effectiveness of these tools for measuring stray light effects on projection display systems. The results of these measurements raise other concerns: How good are the quoted manufacturer specifications? When parameters are specified in a standard or an agreement, how can you be sure that the other parties involved are aware of stray-light problems? Maybe your display performs better than you realize, or possibly you rejected a good projector for the wrong reasons. How can you accurately compare different methodologies if the measurement process is wrought with errors? Boynton and Kelley, along with standards-developing committees such as the VESA Display Metrology Committee, have attempted to help increase awareness by providing simple and meaningful solutions to these common problems.

Contact:

Paul Boynton, 301.975.3014